Modelling Web Navigation by Statechart(5)

UML,OOP,面向对象

Figure6.Screenshot:

Frames

Figure7.Screenshot:MultipleWindowstogether.Framescanbesetscrollableorunscrollable,andeachframemaintainsitsownscrollpositionindependently.Webpagesindifferentframescanaffecteachotherbyusingclientsidescriptsorprograms.Changesthatcanbedoneincludespresentationappearanceandchangingthewebpagedisplayinginanotherframe.Scriptsandprogramsindifferentframesmayalsointeractwitheachothertocre-atecomplicatedreactivebehavior.

3.7NavigationofMultipleWindows

Multiplebrowserwindowscanbeusedtosupportcon-currentviewingofwebpagesinanotherway(Figure7).Windowsdiffersfromframesinthesensethattheycanbecreatedordestroyedindependentlyatdifferenttime,andtheyaremanagedbytheoperatingsystemswindowsman-ager.Clientsidescriptandprogramscanaffectmultiplewindowsinthesamewayasinmultipleframes.

3.8DynamicContent

Thecontentandhyperlinksofawebpagecanbedy-namicwhileviewing.Therearetwolevelsofdynamics,

clientsideandserverside.3.8.1ServerSide

Anexampleofthiskindofdynamicwebpageisthesearchresultpageofasearchengine.Whendifferentsearchstringsareentered,differenthyperlinkswillappearintheresultspagedependingonthekeywordinputedinthesearch.ThiskindofdynamicwebpagegenerationisusedextensivelyintheWWWtoday.

Thisisdonebythewebservergivingoutdifferentwebpagestorequestsofthesamehyperlinktarget(sameURL).UsersactivatingthesamehyperlinkofthesametargettwicemaynotgetthesamereturnedHTML.ServersidescriptsandCGIprogramscanbeusedtogeneratethesewebpages.Atemplateisusedtode nethestructureofthedocumentandcontentis lledinruntime.Thismakesthereturnedwebpagehavesimilarstructurebutwithdifferentcontentandhyperlinks.Notethateveryscriptorprogramcanusemorethanonewebpagetemplateandeverytemplatecanbeusedbymorethanonescriptorprogram.

Serversidedynamicpagegenerationcanalsoemploywebforms,asintheabovesearchengineexample.Thesourcewebpagewillcontainaformwithdata,whentheformissubmittedandthenewpagerequested,theformdataissentalongtothewebserverandanewwebpageisre-turned.Thisisequivalenttoactivatingahyperlinkwithruntimegeneratedparametersinthesourcewebpage,andthenapropertargetwebpageisconstructedinthewebserverandreturnedbasedontheparameters.3.8.2ClientSide

AnexampleofclientsidedynamicwebpageisaJavapro-gramonawebpage.TheJavaprogrammayhaveascrollinglistofhyperlinks,thoselinksscrolledoutofviewcannotbeactivatedwhilethosenewlyscrolledintoviewcanbeacti-vated.

Intheseclientsidedynamicpages,thetargetofahyper-linkcanbedynamicallyde ned,enabled,ordisabledwhileawebpageisdisplaying,withoutcontactingthewebserver.Basedonuserselectionsorotherexternalfactorssuchascurrenttime,thetargetofahyperlinkcanbedifferentwhenitisactivated.Thiskindofwebnavigationissupportedinvariousclientsidescriptsandprograms,suchasJavaScriptandJava.Thesescriptsandprogramshavetheirownstateandreactivebehavior,andcanaffectthecontentandnaviga-tionofthehostingwebpage.Theycannotexecutewithoutahostingwebpage.

Aspecialpropertyoftheseclientsidescriptsandpro-gramisthattheirlifetimeisthesameasthewebpagehost-ingthem.Ifthewebpageisreplacedbyanotherorwindowisclosed,alltheattachedscriptsandprogramswillbeter-minatedimmediately.